Patent application title: Method for the production of panel-type components

Abstract:

The invention relates to a method for the production of panel-type
components (1) having at least three layers of boards (2a, 2b, 2c, 2d,
2e, 2f) disposed parallel to the plane of the component (1), with the
boards being connected to one another without glue by dowels (3)
extending substantially transversely to the plane of the component (1),
with firstly a plurality of layers of boards (2a, 2b, 2c, 2d, 2e, 2f)
being disposed on top of each other in different orientations, a
plurality of bores (5) being provided in these boards (b 2a, 2b, 2c, 2d,
2e, 2f) which penetrate the layers, and the dowels (3) thereafter being
pressed into the bores (5). An especially high strength is achieved in
such a way that the layers of the boards (2a, 2b, 2c, 2d, 2e, 2f), during
drilling and insertion of the dowels (3), are tensioned against each
other by applying compressive forces and that the dowels (3) are
preferably compacted in the radial direction before insertion.

Claims:

1. A method for the production of panel-type components (1) having at
least three layers of boards (2a, 2b, 2c, 2d, 2e, 2f) disposed parallel
to the plane of the component (1), with the boards being connected to one
another without glue by dowels (3) extending substantially transversely
to the plane of the component (1), with firstly a plurality of layers of
boards (2a, 2b, 2c, 2d, 2e, 2f) being disposed on top of each other in
different orientations, a plurality of bores (5) being provided in these
boards (2a, 2b, 2c, 2d, 2e, 2f) which penetrate the layers, and the
dowels (3) thereafter being pressed into the bores (5), wherein the
layers of the boards (2a, 2b, 2c, 2d, 2e, 2f), during drilling and
insertion of the dowels (3), are tensioned against each other by applying
compressive forces and that the dowels (3) are preferably compacted in
the radial direction before insertion.

2. The method according to claim 1, wherein the compressive forces applied
to the boards (2a, 2b, 2c, 2d, 2e, 2f) produce a surface pressing which
is at least so large than the individual boards of adjacent layers rest
in an approximately planar manner on top of each other.

3. The method according to claim 2, wherein the compressive forces applied
to the boards (2a, 2b, 2c, 2d, 2e, 2f) produce a surface pressing which
is at least twice as large as is necessary that the individual boards of
adjacent layers rest in an approximately planar manner on top of each
other.

4. The method according to claim 3, wherein the total force of the
tensioning is larger than half the sum total of forces which are applied
to driving in the dowel (3).

5. The method according to claim 4, wherein the total force of the
tensioning is at least as large as the sum total of forces which are
applied to driving in the dowel (3).

6. The method according to claim 5, comprising a first tensioning Stepp is
performed during the drilling and an additional tensioning occurs prior
to pressing in the dowels (3).

7. The method according to claim 6, wherein tensioning occurs in the
direction of the plane of the panel in addition to the tensioning
perpendicular to the plane of the panel.

8. The method according to claim 7, wherein the dowels (3) are compressed
to a size prior to being driven in that is slightly larger than the cross
section of the bores (5).

9. The method according to claim 8, wherein the dowels (3) are sprayed
with a sliding and/or bonding agent before being driven in.

10. The method according to claim 8, wherein the dowels (3) are introduced
in a dry way into the bores (5).

11. The method according to claim 10, wherein the bores (5) for receiving
the dowels (3) are drilled drill bits with a scavenging passage extending
in the longitudinal direction are used, through which a scavenging medium
is introduced during drilling.

12. A panel-type component (1) consisting of several layers of boards (2a,
2b, 2c, 2d, 2e, 2f) of different orientation disposed parallel to the
plane of the component (1), the boards being connected to one another
without glue by dowels (3) extending substantially transversely to the
plane of the panel, including in the unloaded state the dowels (3) have a
tension in the longitudinal direction.

13. The component according to claim 12, wherein the boards of adjacent
layers are pressed on top of each other by the dowels (3) in an
approximately planar state.

14. The apparatus for producing a component (1) according to claim 13,
comprising drill bits for producing bores (5) which extend substantially
transversely to the plane of the panel and stamps for pressing the dowels
(3) into the bores (5), wherein means are provided for pressing the
components in the axial direction of the bores (5) in order to bring the
boards (2a, 2b, 2c, 2d, 2e, 2f) of the individual layers to an
approximately planar position.

15. The apparatus according to claim 14, wherein the means for pressing
the components (1) are arranged as stamps (17a, 17b) which each enclose
the bores (5).

16. The apparatus according to claim 15, wherein the stamps (17a, 17b) are
arranged annularly.

17. The apparatus according to claim 16, wherein the means for pressing
the components (1) are arranged as pressing beams for pressing over a
large surface area.

18. The apparatus according to claim 17, comprising drill bits and stamps
are held on a portal and a conveying device for conveying the components
(1) is provided which extends through the portal.

19. The apparatus according to claim 17, wherein drill bits and stamps are
held on a displaceable portal.

20. The apparatus according to claim 19, wherein drill bits and stamps are
held at least partly on a robot arm.

21. The apparatus according to claim 20, the drill bits (6) comprise a
scavenging duct (7) extending in the longitudinal direction.

Description:

[0001]The invention relates to a method for the production of panel-type
components having at least three layers of boards disposed parallel to
the plane of the component, the boards being connected to one another
without glue by dowels extending substantially transversely to the plane
of the component, with firstly a plurality of layers of boards being
disposed on top of each other in different orientations, a plurality of
bores being provided in these boards which penetrate the layers, and the
dowels being pressed into the bores.

[0002]It is known to connect wood components by dowels. It is possible in
this context to produce wall elements or the like made from one material,
which means that the connection of the individual components among each
other occurs exclusively through the frictional connection of the
components with the dowels. Examples of walls elements produced in this
manner are provided in EP 1 097 032 A or EP 1 381 740 of the applicant.
If no glue is to be used in the dowel joint, as is required for
ecologically high-value components, it is necessary to produce the
respective holding forces via the frictional connection between the
dowels and the components from which the components are made. This can
occur in the known manner in such a way that dowels are used which have a
diameter which is larger than the bore that are determined for receiving
the dowel. There are limits to hammering or pressing in such dowels
however. A further possibility of improving the frictional connection is
that wedges or the like are driven into the face-side ends of the dowels.
This comes with the disadvantage however that the frictional connection
is improved in this case not over the entire length of the dowel, but
only in the area of the wedges. There is a further disadvantage in that
when the surface is machined which leads to reduction in the thickness of
the components especially the especially supporting parts of the dowel
are removed, leading to an impairment in the quality of the joint.

[0003]It is known from "innovations in wood" in the "Forum Planning June
2003" to produce wood elements by dowel joints, with the dowels being
compressed in the radial direction prior to being driven in. The dowels
are pressed in a rotating manner through a conically tapering opening, so
that the glue grooves, if any, are flattened to a substantial extent.
Although it is possible with such a dowel to improve hold even in case of
humidity changes of the component, the security to be gained is not
sufficient for all applications.

[0004]U.S. Pat. No. 4,474,493 A shows a dowel for producing joints between
components with a slit arranged in a screw-like manner. It is usually not
possible with such a dowel to produce components made of a single
material. Moreover, the forces that can be transmitted by such a dowel
are limited.

[0005]JP 2000-064436A shows a dowel which is compressed prior to being
driven in and increases its volume by taking up humidity. In order to
achieve a secure hold, a relatively strong compression needs to be
performed, which under adverse conditions may lead to damage to
components.

[0006]DE 299 18 118 A shows a wood production component which is connected
by dowels which are arranged parallel to the panel plane. When there is a
bending load, the tensions occurring in the component are absorbed only
by the dowels in the worst case. Such a component is therefore not very
strong.

[0007]A solution is known from SU 1 025 831 A in which individual boards
are arranged perpendicular to the plane of stacks of boards. The dowels
are used to maintain an applied tensioning. The dowels are subjected to
shearing strain. The components thus arranged are primarily suitable as
supports, but not to provide planar components.

[0008]It is the object of the present invention to further develop a
method of the kind mentioned above that a sturdy component with high
loading capacity is created which is insensitive to the various humidity
influences and offers high heat insulation values and high
leak-tightness.

[0009]It is provided in accordance with the invention that the layers of
the boards, during drilling and insertion of the dowels, are tensioned
against each other by applying compressive forces and that the dowels are
preferably compacted in the radial direction before insertion. Boards
within the terms of the present invention are timber which is suitable to
be joined into panel-type components, which also includes timber which is
generally designated as posts. The relevant aspect in the present
invention is that the individual boards are tightly held during the
doweling not only in their position but also tensioned against each other
in the axial direction, i.e. perpendicular to the plane of the board.
This tensioning causes a certain deformation of the boards in the
direction of thickness, which leads to the consequence that after driving
in the dowel a state of tension is maintained. When shearing forces now
occur between the individual layers of the component, as is regularly the
case for example under a bending load or during the occurrence of
shearing forces in the plane of the board which leads to a
parallelogram-like displacement of the element, such shearing forces are
not absorbed in a primarily positive-locking manner by the dowels, but to
a substantial extent by the frictional forces between the individually
layers, which are caused by the inner tension states. In this way,
shearing forces are distributed over the entire surface area and the
loading capability and stiffness of the component will be improved
substantially.

[0010]The compression of the wood dowel can occur for example by three
pressing rollers which are offset by 120°. It is provided that at
least three profiled drive rollers are arranged about the circumference
of a cylindrical spatial area in an approximately similar way for
receiving a dowel, with the drive rollers each being held to rotate about
an axis and the axes being arranged in a skewed way relative to and in a
normal plane on the axis of the cylindrical spatial area.

[0011]The mechanical compression is achieved in this case in such a way
that the milled dowel passes through a press in which three or more
pressing rollers with a concave curved profile are arranged, with the
pressing rollers compressing the dowel in the direction of the diameter.
The profile can be semicircular or also parabolic in the cross section.
The radius of curvature as measured at the apex of the profile should
correspond to the radius of the compressed dowel.

[0012]The tensioning of the boards in the above sense is required in any
case during the doweling locally in the area of the dowel that is
respectively driven in. It is advantageous to apply a certain tensioning
during the drilling in order to no longer substantially influence the
geometry of the bores prior to doweling. It is certainly possible to
apply a low pressure in a planar way during the drilling and to increase
tensioning in the course of driving in the dowel. This additional
tensioning can certainly occur locally in the area of the respective
dowel to be driven in, i.e. in regions where a mutual influence can be
assumed.

[0013]It is similarly not necessary to tension the entire component prior
to doweling. It is certainly sufficient and even preferable when only
those areas of the component are tensioned in which the dowels are
pressed. This reduces the overall required forces and promotes rapid work
progress.

[0014]It is especially advantageous when the compressive forces applied to
the boards cause a surface pressing which is at least so large that the
individual boards of adjacent layers lie one top of one another in an
approximately planar way. The boards which are used in the production of
components in accordance with the invention are usually not ideally
prismatic, but are warped or curved in different ways. In this context,
one can observe curvatures transverse to the direction of the wood fiber,
screw-like twisting and irregular warping. When tensioning has increased
to such an extent that it is ensured that the individual boards can lie
in a planar fashion on top of each other, the required inner tension
state of the component is caused by the reaction forces of the individual
boards which intend to produce the original shape of the individual
boards again. After driving in the dowels, they are subjected to tension
in the longitudinal direction and generate the compressive forces
described above. The fact is also advantageous in this connection that in
this way relatively planar external surfaces are achieved already
directly after the doweling, i.e. in the raw state of the component. It
is then only necessary to remove material in the amount of a few
millimeters in completing the components, in which they are planed down
in order to achieve high surface quality and a completely planar surface.
This not only accelerates the production process as a result of the
reduced duration of the planing process, but also leads to an only
minimal weakening of the cover layers. In the case of major warping of
the outer surface, locally high removal rates would be required which
could lead to a statically critically weakening of the cover layers.

[0015]Usually, the compression in the direction of thickness of the
component will be between 5% and 8% of the thickness of the element. In
the case of starting material of very high quality that has only very
little warpage, one can make do with lower pressings of between 3% and
5%. It is conversely possible that in the case of extremely warped timber
a reduction in the thickness of 15% or more is necessary.

[0016]The production of layers that lie in a planar fashion on top of each
other comes with the additional advantage, in addition to the static
advantages as described above, that large-volume cavities in the interior
of the components can securely be prevented, so that deteriorating heat
insulation values as a result of internal convection flows can be
securely prevented.

[0017]A substantial increase in the transferable forces can be achieved as
a result of additional elastic deformation in the direction of thickness
in such a way that the compressive forces applied to the boards cause a
surface pressing which is at least twice as large as it would be required
that the individual boards of adjacent layers would approximately lie in
a planar fashion on top of each other.

[0018]A further essential criterion for the necessary strength of the
tensioning is given in such a way that the total force of the tensioning
is larger than half the sum total of forces which are applied to driving
in the dowel.

[0019]Typically, the pressing in of dowels with a diameter of 20 mm can
occur with forces which can be up to 20 kN. Smaller forces can suffice in
the case of lower requirements placed on production speed or in the case
of a lower overdimensioning of the dowel. It has been seen that a tension
of the dowels in the finished component can then be achieved in a secure
manner when the sum total of pressures applied over large surface areas
and pressures applied locally about the driving-in position is at least
half of this force. Especially preferably, the tensioning can be larger
than the driving forces of the dowels.

[0020]It has been noticed that it is advantageous when the dowels are
compressed prior to driving in to a size which is only slightly larger
than the cross section of the bores. The force between dowel and the
surrounding boards consists of two components, which are on the one hand
the force which arises already from the difference in dimension during
the driving in and on the other hand from the additional force which
arises when the dowel tries to expand from the originally compressed
state.

[0021]It is especially advantageous when the dowels are sprayed with a
sliding and/or bonding agent before being driven in. Casein is used for
example as such a sliding and bonding agent. Ideally, it is ensured by
spraying the dowels that the driving is facilitated as a result of the
reduced frictional forces, bonding between dowels and boards is increased
in the end state and, most of all, an immediate swelling is produced as a
result of the increased humidity directly after driving in the dowels.
This leads to the consequence that the component can be subjected to
higher loads directly after doweling and can therefore be manipulated
more easily in the production process. As an alternative to this it is
also possible to introduce the dowels in a dry manner into the bores,
which enables a simplification of the production process.

[0022]An especially advantageous embodiment of the method in accordance
with the invention provides that when the bores are drilled drill bits
with a scavenging passage extending in the longitudinal direction are
used during drilling, through which a scavenging medium is introduced
during drilling such as compressed air. It is relevant for performing the
method in an economical way to introduce a large number of bores in a
short period of time. Since the thickness of the components can be up to
400 mm and more, the introduction of the bores is problematic, especially
when this should occur in a single pass. Blockages of the conveying
grooves of twist drills and strong heating of the drill bits occur,
leading to an impairment of the wood material in the area of the bore.
This leads to an impaired seating of the dowels. By introducing a
scavenging medium along the longitudinal axis of the bore, it is possible
on the one hand to prevent blockages of the spiral ducts, so that chips
can be removed securely. Moreover, an impairment of the bore wall is
prevented by the cooling effect.

[0023]The present invention further relates to a panel-type component
which consists of several layers of boards of different orientation which
are connected with each other without glue by dowels extending
substantially transversally to the plane of the panel.

[0024]The component in accordance with the invention is not limited that
all dowels extend exactly normally to the plane of the panel. In various
applications such as elements subjected primarily to bending stresses for
example as are used in the area of ceilings it may be advantageous to
also introduce dowels in an oblique position. The advantages as explained
above may also be achieved in components of this type.

[0025]It is provided in accordance with the invention that the dowels have
a tension in the longitudinal direction. The inner tensional state of the
component ensures, as described above, a substantial increase in the
strength, as well as the leak-proofness of the component. Preferably, the
component in accordance with the invention is characterized in that the
boards of adjacent layers are pressed against each other by the dowels in
an approximately planar state. The relevant aspect is that this state
that lies approximately planar above one another is also achieved in
cases where the boards are not delimited prior to processing by an
exactly plane and parallel surface.

[0026]The present invention further relates to an apparatus for producing
a component of the kind mentioned above with drills for producing bores
which extend substantially transversely to the plane of the panel and
with stamps for pressing the dowels into the bores.

[0027]In accordance with the invention, this apparatus is characterized in
that means are provided for compressing the components in the axial
direction of the bores. The compression can occur globally on the one
hand, i.e. over a large surface area, such that the individual layers of
the massive wood components of a component to be doweled are tensioned by
respective tensioning elements by pressing beams transversally to the
plane of the component. Typical surface pressures lie between 5
N/cm2 and 30 N/cm2. It has proven to be especially advantageous
however to perform the compression locally, i.e. in the area around the
dowel with higher pressing pressures. Surface pressing typically can be
between 30 N/cm2 and 200 N/cm2 and is preferably at
approximately 100 N/cm2. It is advantageous when the means for
compressing the components are arranged as stamps which each enclose the
bores. Pressing is achieved for example by stamps with an annular
pressing surface which are pressed centrally about each bore against the
workpiece.

[0028]An optimum can be achieved by a combination of these two kinds of
compression. Not only are the individual pieces to be joined kept exactly
in the desired position so that warping on the finished component is
avoided for example, but the type of transfer of forces by the dowels is
especially changed to a relevant extent for example. Shearing forces in
the plane transversally to the axis of the dowels are no longer primarily
transferred by shearing to the dowels, but relevantly by frictional
forces between the individual layers of the pieces to be joined which are
based on normal forces which are caused by tensions in the dowels.

[0029]The apparatus in accordance with the invention can be arranged in
various ways. Most advantageously it is characterized by a portal on
which the apparatuses for drilling and for pressing in the dowels are
arranged. The individual components are guided through the portal step by
step and processed. Alternatively, it is similarly possible to move a
displaceable portal over the components. As an alternative to such
portals or in addition to these it is possible to provide robots which
make the bores and press in the dowels. It may be especially advantageous
in connection with a portal for example to provide robots and to
introduce dowels inclined to the normal direction of the plane of the
panel.

[0030]The present invention is now explained below in closer detail by
reference to the embodiments shown in the drawings, wherein:

[0031]FIG. 1 shows the principal arrangement of a panel-type component;

[0035]The panel-type component 1 which is shown in FIG. 1 consists of a
total of six layers of boards 2a, 2b, 2c, 2d, 2e, 2f which are arranged
in different orientation with respect to each other. The boards 2a, 2b,
2c, 2d, 2e, 2f are joined with each other without glue by dowels 3.

[0036]FIG. 2 shows the principal arrangement of an apparatus in accordance
with the invention. A carriage 7 which is displaceable in the
longitudinal direction is arranged on the machine bed 6, on which the
panel-type components 1 are placed. A device carrier 8 in the form of a
portal is fixed above the carriage 7, which carrier is supported by
pillars 9. Drilling devices 10 on the one hand and dowel driving
apparatuses on the other hand are incorporated on the device carrier 8.
It is thus possible that a plurality of bores is introduced in the
component 1 in a few job steps. It is similarly possible to press in
several dowels simultaneously into the previously produced bores. The
pressing in occurs for example pneumatically with a pressure of 120 bar
at a dowel diameter of 20 mm.

[0037]In order to achieve and improve a strength the component 1 which
meets the static requirements, which component is arranged as a massive
wood component, dowels 3 are mechanically compacted prior to the
mechanical pressing into the component 1, so that its diameter decreases
by 2% to 20%. Such dowels 3 will swell more strongly after the pressing
into bores 5 of component 1 than conventionally milled wood dowels, even
they are introduced in a drier state than the wood of component 1. In
addition, the diameters d of the bores 5 can be provided with a smaller
arrangement than the diameter D of dowel 3. The difference between the
diameter D of dowel 3 and the diameter d of bores 5 can be up to 20% of
the diameter d of the bores 5. The dowels 3 are pressed mechanically into
the bores 5 which are provided with a smaller diameter.

[0038]It is known to increase the frictional connection of the dowels 3
relative to the ambient wood layers by humidity difference (technical
pre-drying of dowels 3). This effect can also be applied in the method in
accordance with the invention. This leads to the ecological, technical
and economical advantage that conventional synthetic gluing of the dowel
3 or mechanical aids such as wedging on the face side, etc. can be
omitted.

[0039]In order to improve the sliding capability during the pressing
process, water or also a gluing fluid as an additional static security
means can be sprayed on. The composition of said fluid can consist of
ingredients that are safe for foods within the terms of a product that is
compatible with ecological building standards. The pre-pressed dowel 3
can also be introduced in a dry state into the component 1.

[0040]During the drilling and doweling, the boards 2a, 2b, 2c, 2d, 2e, 2f
of the component 1 are pressed downwardly and clamped by the clamping
elements 16a, 16b. Any bulging or warping or other curvatures of the
individual boards 2a, 2b, 2c, 2d, 2e, 2f are eliminated in this process
and an approximately planar position is produced. The clamping is
released only after the dowels 3 have been driven in.

[0041]FIG. 3 shows that the means for clamping are arranged on the one
hand as pressing beams 16a for pressing over a large surface area and on
other hand as annular stamps 17a. The annular stamps 17a are arranged
concentrically about the bores 5 to be produced and ensure an especially
favourable pressing in the direction of arrows 18 in this critical
region. Reference numerals 16b and 17b indicate respective
counter-holders which can also be integrated in table 7.

[0042]FIG. 4 shows a drill bit 26 which is especially suitable for use in
the apparatus in accordance with the invention. Drill bit 26 is arranged
per se in the form of a conventional twist drill, but has a scavenging
duct 27 extending in the longitudinal direction which opens forwardly at
the tip of the drill bit into an opening 28. In this way, a liquid or
gaseous scavenging medium can be blown forwardly which cools the drill
bit 26 and removes the chips.

[0043]It is possible with the method in accordance with the invention and
the apparatus in accordance with the invention to produce panel-type
components of high strength in a simple and cost-effective way.